Automotive body panels are typically produced by forming low carbon steel or aluminum alloy sheet stock into desired panel shapes, often by conventional room temperature processes such as stamping. Such body panels, however, can also be produced by hot gas blow-forming processes, such as SPF. Compared to conventional stamping processes, SPF processes are capable of producing more complex panel shapes from a single sheet of material. SPF processes involve complex integrally heated presses and low material deformation rates that yield cycle times typically between 20 and 60 minutes. Such relatively long cycle times are incompatible with automotive production rates. Also, because SPF heat sources are remotely located from SPF forming tool surfaces, SPF processes do not provide a high degree of temperature control at the workpiece.
Therefore, QPF processes were developed to reduce the cycle time of SPF and to provide better temperature control closer to forming tool surfaces by attaching insulation to, and embedding heating elements within, the forming tools themselves. Providing insulation and heating elements in each forming tool, however, requires a lead time to produce QPF forming tools and increases the costs thereof. Such investment costs are recoverable by suitable production volumes. With lower volume production runs, however, internally or integrally heated hot forming tools may be too expensive.
Accordingly, SPF and QPF processes are not optimized for every type of hot gas blow-forming production situation including low cycle time prototyping or other low-volume production. Thus, there is a need for a hot gas blow-forming apparatus that avoids the expense and lead times associated with integrally heated tooling, and avoids the long cycle times and lack of localized temperature control of SPF heated press processes.